A wide variety of implantable medical devices (IMDs) for delivering a therapy and/or sensing a physiologic condition of a patient have been clinically implanted or proposed for clinical implantation in patients. Such IMDs may deliver therapy and/or monitor the heart, muscle, nerves, brain, stomach or other organs. In some cases, the IMDs deliver electrical stimulation therapy to the patient and/or monitor physiological signals of the patient via one or more electrodes or sensor elements, at least some of which may be included as part of one or more elongated implantable medical leads coupled to the IMD. Implantable medical leads may be configured to allow electrodes or sensors to be positioned at desired locations for delivery of stimulation or sensing physiological signals. In some cases, electrodes or sensors may be positioned on an IMD housing as an alternative or in addition to electrodes or sensors deployed on one or more leads.
For example, implantable cardiac devices, such as cardiac pacemakers or implantable cardioverter defibrillators, provide therapeutic electrical stimulation to the heart by delivering electrical therapy signals such as pulses or shocks for pacing, cardioversion or defibrillation via electrodes of one or more implantable leads. In some cases, such an IMD may sense intrinsic depolarizations of the heart, and control the delivery of the electrical therapy signals to the heart based on the sensing. When an abnormal rhythm is detected, such as bradycardia, tachycardia or fibrillation, an appropriate electrical therapy (e.g., in the form of pulses or shocks) may be delivered to restore the normal rhythm. For example, in some cases, the IMD may deliver pacing, cardioversion or defibrillation therapy to the heart of the patient upon detecting ventricular tachycardia, and deliver cardioversion or defibrillation therapy to a patient's heart upon detecting ventricular fibrillation.